High performance device for balancing a force

ABSTRACT

A device for balancing a force. The device includes an articulated mechanism ( 10 ). The articulated mechanism ( 10 ) includes a proximal arm ( 12 ) borne by a support wedged on a first hinge pin ( 20 ) and a distal arm ( 14 ) borne by the proximal arm and wedged on a second hinge pin ( 24 ) extending parallel to the first pin. The distal arm has a free end ( 26 ) supporting a load (F). The device further includes first balancing means ( 18,20 ) with high bandwidth acting on the proximal arm ( 12 ), second balancing means ( 18,22 ) with high bandwidth acting on the distal arm ( 4 ), and coordinating means interposed between the first balancing means and the second balancing means to coordinate rotational movements of the proximal arm and the distal arm.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase Patent Application of InternationalApplication Number PCT/FR01/02835, filed on Sep. 12, 2001, which claimspriority of French Patent Application Number 00/11733, filed Sep. 14,2000, and French Patent Application Number 00/15586, filed Dec. 1, 2000.

The invention relates to a device for balancing a force, which iscapable of guiding a load over a given trajectory, in particular alinear trajectory.

Balancing devices of this type are already known which comprise anarticulated mechanism formed by a proximal arm carried by a support andkeyed on a first hinge pin and a distal arm carried by the proximal armand keyed about a second hinge pin extending parallel to the first pin,the distal arm having a free end carrying a load.

A balancing device with two articulated arms of this type has numerousapplications, in particular in the field of handling devices, transferdevices, etc. It may also be used as a pantograph, in particular arailway pantograph for electric locomotives.

Various solutions are already known for balancing the load carried bythe articulated mechanism.

In the first instance, pneumatic solutions are known which employ a jackfor suspending and/or moving the load, for example in a verticaldirection.

Although these solutions give relatively satisfactory results with lightloads, they become impossible to manage once the volume of air in thejack exceeds about 1 dm³. This is due to the losses of loads which leadto pressure variations between the various points of the circuit and tothe compressibility of air. Pneumatic means of this type have thedrawback of having a response time of approximately 1 second, and thiscorresponds to a mediocre bandwidth value, in other words a time whichis too great not to be felt, in particular by an operator.

Mixed solutions are also known, in which a pneumatic system is coupledto a counterweight. These solutions, which lead to the same results asthe previous solutions, also have the drawback of a significant increasein the inertia, and this may also affect the horizontal movements of theload.

In addition, electrical solutions are known which generally involve theuse of types of tackle with automatic load control. These solutions havethe drawbacks, on the one hand, of sophisticated systems (risk ofbreakdown) and, on the other hand, of requiring a weighing phase duringwhich the load is not controlled and may be dangerous for the operator.These solutions have the further drawback of having a long response timewhich is incompatible in practice with convenient handling on account oftheir low bandwidth. This applies, in particular, if this movementnecessitates the control of a position which is not representedphysically, and hence the presence of a position loop.

Furthermore, solutions employing a parallelogram are known, as definedin French patent application No. 00 03047, and have the drawbacks, onthe one hand, of not effecting guidance (as with a cable) or ofnecessitating an arcuate trajectory in a vertical plane and, on theother hand, of concentrating all the forces associated with the weighton a single arm of the parallelogram. The solution described in Frenchpatent No. 96 07556 employs a parallelogram but does not comprise ameans of coordination. Therefore, the bandwidth of the assembly cannotbe taken for granted, whatever the quality of the balancing means.

The object of the invention is, in particular, to overcome theaforementioned drawbacks.

It aims, in particular, to provide a high performance device forbalancing a force, for guiding a load over a trajectory with a highbandwidth.

Accordingly, it proposes a device for balancing a force of the typedefined at the outset, which comprises first high bandwidth balancingmeans having a first output shaft and acting on the proximal arm, secondhigh bandwidth balancing means having a second output shaft and actingon the distal arm as well as high bandwidth coordinating meansinterposed between the first balancing means and the second balancingmeans to coordinate the respective rotational movements of the proximalarm and of the distal arm.

Therefore, the invention allows the proximal arm and the distal arm ofthe articulated mechanism to be balanced separately, owing to firstbalancing means and second balancing means which are coordinated withone another. This minimises the inertia brought back to the balancingsystem and the elasticity of transmission of the proximal arm and thedistal arm.

These balancing means have a high bandwidth, meaning a bandwidth ofabout 100 Hertz, without adding considerable friction and inertia.

As a reminder, the bandwidth translates the ability of a mechanicalsystem to react to transient phenomena. In practice, it translates theability of said system to maintain its performance when subjected tostresses which, in the present case, may be of approximately 100 Hertz,and this may also be defined as a response time of approximately 100thof a second.

In the scope of the invention, various types of balancing means may beused, including motorisation means in certain cases.

In a preferred embodiment of the invention, the device comprises abalancer capable of providing a sinusoidal mechanical torque and havingtwo output shafts which have speeds of rotation which are synchronisedbut in opposite directions, and in which these output shafts arerotationally engaged with the first hinge pin of the proximal arm andwith the second hinge pin of the distal arm respectively.

By way of example, a balancer of this type may be of the type describedin French patent No. 88 02 423 (published under No. 2 627 718).

A known balancer of this type, which is purely mechanical, is generallyused to balance the forces acting on an arm acted upon by a load such asa tool. It results in strict balancing of the arm, whatever its angularposition, and is capable of pivoting by 360°, allowing the load todescribe a circular trajectory.

This known balancer affords the advantage of providing a sinusoidaltorque with an excellent yield and a high bandwidth, in other wordsmechanical balancing with a short response time.

Therefore, when the two output shafts of the balancer are rotationallyengaged with the hinge pin of the proximal arm and the hinge pin of thedistal arm respectively, the balancing device according to the inventionallows synchronous movement of the two arms during a single manoeuvre ofthe load, whatever the distribution of the loads on each of the two armsof the articulated mechanism.

Preferably, one of the two output shafts of the balancer forms the hingepin of the proximal arm whereas the other output shaft is coupled to thehinge pin of the distal arm by transmission means.

Various mechanical means may be used for this purpose, in particularmeans having at least one deformable parallelogram.

According to a further characteristic of the invention, the proximal armand the distal arm are the same length.

As a result, the load is able to move over a rectilinear trajectory witha range of movement corresponding to four times the length of each ofthe aforementioned arms.

According to a further characteristic of the invention, the devicecomprises an additional motorisation means formed by at least oneactuator coupled to at least one moving part of the device.

A motorisation means of this type may be used to move the articulatedmechanism from one of two positions, which include a service positionand a storage position, to the other.

Preferably, these adjustment means comprise a mass which is capable ofmoving on the proximal arm or the distal arm.

The invention also provides that the device may comprise an additionalmotorisation means controlled by a force sensor placed at a positionwhich is selected for assisting an operator in the case of a manualmovement or for applying a constant force to a given part.

In a preferred application of the invention, the free end of the distalarm carries the bows of a railway pantograph capable of collecting theelectrical energy from a catenary such that the load here is formed bythe force exerted on the catenary by the bows.

In the case of application to a railway pantograph, it is advantageousif the device comprises at least one accessory, in particular anaerofoil, which is rotationally engaged with the second output shaftwhile being mounted either on this second output shaft or idly on thefirst output shaft, which has selected geometry and moves parallel tothe distal arm with which it is rotationally engaged, this accessorybeing disposed on a radius of gyration such that its penetration of theair generates a torque equal and opposed to the torque of penetration ofthe air of the articulated mechanism (in other words of the pantographhere), these two torques cancelling one another in the connectingmechanics. A pantograph which is insensitive to the wind speed isproduced in this way.

As mentioned hereinbefore, the balancing means of the invention, in avariation, may comprise motorisation means.

In a further embodiment intended, in particular, for a railwaypantograph, a servocontrol motorisation means provides inertial forcesassociated with the movement, on the vertical axis, of the entirety ofthe structure. This is intended to prevent the force produced by thebows on the catenary from being disturbed by these movements. Thisservocontrol motorisation means will also be capable of compensating theimperfection of the torque defined by the abovementioned aerofoil oreven to make up for its absence. This motorisation means comprises anelectric motor coupled to an endless screw cooperating with a nut, thisnut being carried by a crank coupled to either the first output shaft orthe second output shaft, the servocontrol means being provided tocontrol the electric motor on the basis of a control signal transmittedby a force sensor carried at the free end of the distal arm.

The endless screw is advantageously a reversible screw driven by theelectric motor via a reduction gear, a clutch mechanism being interposedbetween the reduction gear and the endless screw.

The presence of this reduction gear allows the use of a large-pitchreversible endless screw with a high reverse yield. However, a screwhaving a smaller pitch, but no reduction gear, may also be considered.

The servocontrol means advantageously comprise a tachymetric dynamodriven by the electric motor and capable of transmitting a speed signal,a first operational amplifier (speed loop) receiving this speed signaland producing a first output signal, a second operational amplifier(current loop) receiving the first output signal and transmitting asecond output signal, a power amplifier receiving this second outputsignal and transmitting an output current sent to the electric motor andfrom which the image of this output current is sent to the secondoperational amplifier, the control signal transmitted by the forcesensor being applied to the input of the second operational amplifier(current loop).

It is also advantageous that the servocontrol motorisation means may beused as an ancillary system for the unfolding and folding operation.

This unfolding and folding mechanism is of particular interest when thefree end of the distal arm carries the bows of a railway pantograph.

Preferably, this mechanism is capable of receiving a control signalapplied to the first operational amplifier (speed loop) to bring aboutthe folding or unfolding of the articulated mechanism. This signal willthus have priority over the signal from the force sensor brought back tothe current loop.

It is also advantageous that this mechanism is capable of receiving anemergency signal applied to the first operational amplifier (speed loop)to bring about the folding of the articulated mechanism in an emergency.This signal will also have priority over the signal from the forcesensor, brought back to the current loop.

This priority of the speed loop over the current loop prevails each timethat the force of the bows on the catenary disappears for a significanttime.

According to a further characteristic of the invention, the servocontrolmeans comprise corrective means capable of performing a correctiveaction between the control signal transmitted by the force sensor andthe actual force applied to the load, in order to compensate theinertial forces associated with the mechanics placed downstream of thesensor, in particular with the mass of the bows in the case of a railwaypantograph. These corrective means comprise differentiating meanscapable of differentiating the speed variations recorded on thetachymetric dynamo over time and applying them to the input of thesecond operational amplifier.

A further ancillary drive system distinct from the system describedhereinbefore will allow the folding of the pantograph in the event of abreakdown of this first system.

In the following description, given merely as an example, reference willbe made to the accompanying drawings, in which:

FIG. 1 is a diagram of a balancing device according to a firstembodiment of the invention;

FIG. 2 is a diagram of a balancing device according to a secondembodiment of the invention;

FIG. 3 is a side view of a balancing device according to a thirdembodiment of the invention applied to a railway pantograph;

FIG. 4 is a front view corresponding to FIG. 3;

FIG. 5 shows the motorisation means according to the invention;

FIG. 6 is a view similar to FIG. 3 incorporating the motorisation meansof FIG. 5; and

FIG. 7 shows a servocontrol circuit forming part of the motorisationmeans of FIGS. 5 and 6.

The balancing device shown in FIG. 1 comprises an articulated mechanism10 formed by a proximal arm 12 and a distal arm 14. The proximal arm 12is carried by a support 16 formed here by the frame or body of abalancer 18.

This balancer is advantageously of the type described in theaforementioned French patent No. 88 02423. It comprises two output pinsor shafts 20 and 22 which are mutually parallel and, in the example,disposed horizontally. The balancer is capable of providing a sinusoidaltorque and the two output shafts 20 and 22 are connected so as to havesynchronised speeds of rotation, but in opposite directions.

The output shaft 20 is coincident with the hinge pin of the proximal arm12. The distal arm 14 is carried by the proximal arm 12 and is keyedabout the hinge pin 24 which extends parallel to the output shaft 20.

The distal arm 14 has a free end 26 capable of providing a force F andan opposite end 28 forming a hinge pin.

The proximal arm 12 is fixed to the output shaft 20 of the balancer 18and is therefore rotationally engaged therewith.

A crank 30 is fixed to the output shaft 22 of the balancer and is alsorotationally engaged therewith. As a result, the proximal arm 12 and thecrank 30 rotate synchronously but in opposite directions.

A crank 32 is fixed on the output shaft 20 by bearings (not shown) whichenable it to rotate freely on this shaft.

Furthermore, a connecting link 34 is fixed to the ends of the cranks 30and 32 by bearings (not shown) which allow rotation and thus create aparallelogram which transmits the forces of the crank 30 to the crank32.

The distal arm 14 is fixed to the end of the proximal arm 12 by bearings(not shown) which allow it to pivot freely and without stress about thepin 24.

The arm 14 has a length L between its end 26 and the hinge pin 24 whichis equal to the length of the arm 12, as defined between the shaft 20and pin 24.

A connecting rod 36 parallel to the proximal arm 12 is fixed on one sideto a crank 38 and on the other side to the end 28 of the distal arm 14via bearings (not shown), thus creating a second parallelogram whichtransmits the forces of the crank 38 to the distal arm 14. The cranks 32and 38 are fixed to the output shaft 20 and are mounted freely rotatablyabout it but are rotationally engaged with one another, forming an angleA capable of preventing buttressing.

The output shafts 20 and 22 are synchronised in opposite directions andare indexed so that when the arm 12 is horizontal, the crank 38 is alsohorizontal (in either direction, depending on whether the connecting rod36 is below or above the arm 12). As a result, the rotation of theoutput shafts 20 and 22 through 180° causes the free end 26 to movealong a straight line over a distance or range equal to 4×L. Thisstraight line corresponds to a rectilinear trajectory T which extendsvertically in the example.

It will be appreciated that the variable angle bisector formed by thearms 12 and 14 therefore remains parallel to itself.

As the balancer 18 provides a sinusoidal torque, the force F transmittedto the end 26 is constant and always parallel to the direction indicatedby the arrow. This force is equal to the sum of the maximum torques (arm12 horizontal) given by the balancer 18 at the output shafts 20 and 22while being reduced by the torque brought back by the weights of thevarious moving elements (arms, connecting rods, cranks, connectinglinks, plain or rolling bearings, etc. plus various on-board systems ortools) divided by the value 2×L (except when the arms 12 and 14 arevertical, upward or downward, where a buttressing phenomenon occurs.

This force may be used to balance a mass which will therefore beweightless over the entire trajectory T (a vertical trajectory here), orelse to apply a force, for example the force which a current-collectorpantograph bow must exert on a catenary.

The device in FIG. 2 comprises the basic elements of the device in FIG.1, like elements being designated by like reference numerals. It alsoincludes an additional motorisation means 40 applied, in the example, tothe connecting link 34 and usable for different purposes.

This additional motorisation means may be used, in particular, to movethe articulated mechanism 10 from one of two positions, including aservice position and a storage position, to the other. This motorisationmeans will be neutralised when the device is in the service or operatingposition.

In a variation, this additional motorisation means may also be used tobalance additional masses which will not always be present or of whichthe weights are substantially different or to compensate an absence ofadditional mass. As an example, the main mass could be a gripper and theadditional masses could be various parts, the motorisation means 40being limited to the weight of the part present.

This additional motorisation means could also be used to make the end 26pass through the desired movements, the motorisation means being limitedto friction and inertia, to the exclusion of the out-of-balance load.

Any combinations of ancillary, balancing of additional masses andmotorisation means may also be used.

If necessary, the device may be combined with a device for controllingan mechanical handling means with servocontrol, as taught by Frenchpatent application No. 0003047 in the name of the Applicants.

It will be appreciated that the additional motorisation means 40 may beof any type (pneumatic, hydraulic, electrical, etc.), linear orcircular. In addition, its point of application is not limited to theconnecting link 34 and it may be any part associated with the movement,including the output shafts 20 and 22 and even the free end 26 of thedistal arm.

Furthermore, the device of FIG. 2 comprises means capable of imparting aconstant orientation to a connecting link 42 carrying the load (forceF). This connecting link 42 therefore extends in the direction of theaforementioned trajectory T.

This device comprises a crank 44 fixed to the end of the proximal arm 12by rolling bearings and therefore freely rotatably relative thereto. Atits lower end, this crank 44 carries an elongate part 46 comprising anoblong hole in which there slides a finger 48 fixed on the connectingrod 36 vertically to the hinge pin 24. When the finger 48 slides in theoblong hole, owing to the deformation of the parallelogram formed by thearms 12 and 14, the connecting link 38 and the connecting rod 36 duringoperation, the crank 44 remains vertical. A connecting rod 50 is fixedby rolling bearings, therefore freely rotatably, at one end to the crank44 and, at its end, to the connecting link 42 so as to remain parallelto the arm 14 and therefore form a deformable parallelogram.

It is obviously possible to replace this sliding finger-type device witha parallelogram which seeks a given direction, possibly the verticaldirection, between the output shaft 20 and a fixed point.

For certain applications, it is possible to construct, on the connectinglink 42, a tool (not shown) which maintains a predetermined orientationwhatever the position of its centre of gravity, and, in particular, apart-gripping tool which allows changes of orientation of this part.

It should be noted that the variation of the load or of the forcedesired at the end 26 (FIG. 1) may be achieved, not only via themotorisation means 40, but via the movement of a load along one of thearms 12 and 14. This movement may be effected by hand or by amotorisation means. It allows the mechanical torque associated with theweight of the moving elements and brought back to the device 18 to bemodified.

Referring now to FIGS. 3 and 4, a balancing device according to theinvention is shown which resembles that in FIG. 2 and is applied to apantograph of a railway power unit. The elements common with those inFIG. 2 are designated by the same reference numerals. The device carriestwo railway bows 76 and 78 capable of coming into contact with acatenary (not shown).

This embodiment aims to improve the behaviour in horizontal forces, inparticular those induced by the resistance to penetration through theair.

The actual structure of the pantograph allows excellent behaviour withregard to the lateral forces which occur perpendicularly to thedirection of advance of the railway power unit, and this does not poseany particular problems.

A problem arises more specifically with regard to the forces created inthe direction of travel of the railway power unit.

A balancer of the type described in the aforementioned French patent No.88 02423 provides high values of direct and indirect yield, in otherwords values of approximately 98%. The high bandwidth of these mechanicsimparts to the pantograph very good transfer of torque from one of theoutput shafts to the other. In fact, as these output shafts rotate inopposite directions, the balancer will reverse the direction of thetransferred torque, from one output shaft to the other. Thischaracteristic therefore allows a certain amount of stability to beimparted to the entire structure.

The device according to the embodiment in FIGS. 3 and 4 differs fromthat in FIG. 2 with regard to the means capable of imparting a constantorientation to the connecting link 42. The elongate part 46 comprisingan oblong hole (FIG. 2) is replaced by a tie rod 80 which seeks itsdirection on the frame of the balancer.

In this case, the force created by the penetration of the bows 76 and 78and of their supports through the air, as well as the friction on thecatenary, do not affect the behaviour of the pantograph on the verticalaxis. This is valid for all the mechanics situated at the end of thedistal arm.

On the other hand, the force of penetration through the air of theproximal arm 12 and the distal arm 14 is not completely compensated. Atorque equivalent to that produced by the force of penetration of thedistal arm 14 applied to the end of the proximal arm 12 remains on theoutput shaft 20 (which supports the proximal arm).

This therefore results in either an increase or a reduction in the forceexerted on the catenary by the bows, depending on the direction oftravel of the power unit. This phenomenon therefore impairs goodoperation of the pantograph and should be taken into consideration sothat it may be cancelled or so that its effects may at least be reduced.

A first solution would involve placing, on the second output shaft 22 ofthe balancer, a structure equivalent to that of the articulatedmechanism carried by the first output shaft 20 and which would thereforecreate the same torque, these two torques cancelling one another out inthe balancer.

A solution of this type comprises several drawbacks, in particular anincrease in the weight of the structure, an increase in its inertia andtwice the bulk when the pantograph is folded. What is more, thissolution is very expensive.

To solve this problem, the invention proposes a further solution whichinvolves modelling this second structure and replacing it with anaccessory, in particular an aerofoil, which is aerodynamicallyequivalent to this second structure.

Referring to FIGS. 3 and 4, an accessory 82 of this type, of theaerofoil type here, is shown which has selected geometry and movesparallel to the distal arm 14 with which it is rotationally engaged.

This accessory 82 is disposed on a radius of gyration R such that itspenetration through the air generates a torque equal and opposed to thetorque of penetration through the air of the articulated mechanism 10(pantograph), these two torques cancelling one another out in theconnection mechanics of the balancer 18.

In the example, the accessory 82 comprises a profile 84 which forms anactual aerofoil and is fixed to the end of two levers 86 rotationallyengaged with the cranks 30.

As a result, these two levers are set into rotation at the same time asthe proximal arm, but in the opposite direction.

It has been seen hereinbefore that the residual torque was created by aforce corresponding to the penetration through the air of the distal armand applied to the end of the proximal arm.

The accessory 82 which is rotationally engaged with the second outputshaft of the balancer provides identical frictional conditions as ittakes to the air at the same angle as the distal arm with which it isalso rotationally engaged and the variations of its lever arm areperfectly symmetrical with those of the proximal arm. It thereforecreates a torque which is equivalent in type and value to the residualtorque due to the penetration of the pantograph structure through theair. These two torques therefore cancel one another out through themechanics of the balancer.

This modelling will obviously be adjustable, in particular with regardto the structure and geometry of the aerofoil and its radius ofgyration, depending on the aerodynamic characteristics of the power unitand the pantograph.

In addition, the attachment of this system is complementary to all thepoints mentioned hereinbefore with reference to FIGS. 1 and 2, inparticular the installation of a servocontrol system for forces (see themotorisation means 90 described hereinafter), the adjustment of which itfacilitates by limiting its role to control of the inertia of thepantograph.

The attachment of this accessory does not significantly affect theoverall inertia of the pantograph. Its weight is fully accounted for bythe balancer.

Finally, this accessory allows correction of the distortion due to thefact that, contrary to the hypotheses taken in the calculation andalthough the distal arm and the proximal arm have the same length, theforce of penetration through the air of the distal arm is not identicalto that of the proximal arm, in particular on account of the presence ofa cowling on the power unit and of the connecting rod 36.

In a variation, the accessory may be mounted on the crank 32 which is inturn rotationally engaged with the second output shaft of the balancer,this arrangement reducing the bulk of the folded accessory. In thiscase, the accessory is mounted idly on the first output shaft 20.

More generally, any means of compensating the force of penetrationthrough the air by the structure of the pantograph, rotationally engagedwith the second output shaft of the balancer, may be disposed either onthe first output shaft or on the second output shaft of the balancer oreven on both.

The structure of the accessory is not limited to an aerofoil, as shownin FIGS. 3 and 4, but may resemble a structure closer to that of thedistal arm, whose penetration through the air it models.

Referring now to FIG. 5, the motorisation means 90 used for theservocontrol of the articulated mechanism 10 are shown, this mechanismadvantageously consisting of a railway pantograph, as shown in FIG. 6.

These motorisation means with servocontrol are advantageously combinedwith a mechanical balancer 18 having two output shafts 20 and 22 asdescribed hereinbefore. These motorisation means 90 comprise an assemblywhich is articulated about a pin 92 and includes an electric motor 94coupled to a tachymetric dynamo 96. Via a reduction gear 98 and a clutch100, this motor 94 drives an endless screw 102 which cooperates with anut 104. This nut 104 is articulated at 106 to the end of a crank 108which is coupled to one of the output shafts 20 and 22 of the balancer18. Advantageously, this coupling will insulate the electrical potentialof the balancer (that of the catenary) from that of the endless screw(mass of the power unit).

A servocontrol circuit 110 which will be described hereinafter withreference to FIG. 7, controls the electric motor 94 on the basis of acontrol signal SC transmitted by a force sensor 112 carried at the freeend of the distal arm 14 of the articulated mechanism 10. As mentionedhereinbefore, these motorisation means are advantageously used in thecase of a railway pantograph, as shown in FIG. 6. The pantograph of FIG.6 corresponds to that of FIGS. 3 and 4. In this particular example, therailway pantograph comprises an aerofoil 82 similar to the one describedhereinbefore. The crank 108 is advantageously rotationally engaged withthe aerofoil, in other words more particularly the levers 86 which arerotationally engaged with the output shaft 22 of the balancer 18.

The installation of this servocontrol means is intended, in particular,to address the problem of the dissociation of systems which generatepressures on the catenary 74 and control of the inertia of thepantograph structure. This is intended to overcome variations inparallelism between the catenary and the railway, whether they are dueto the actual geometry of the line or to the oscillations which thepassage of a first pantograph causes on the catenary and which have tobe followed by any following pantographs.

These servocontrol motorisation means are mounted on the mechanicalbalancer 18 in the example. A mechanical balancer of this typeintrinsically creates a sinusoidal torque which balances 98% of the massof the structure. In the case of the pantograph, the induced kinematicsfor their part intrinsically create the force on the catenary with thesame precision, whatever the unfolded position of the pantographstructure. In addition, low inertia and friction values of the balanceras well as its high bandwidth make it particularly suitable for amotorisation means of this type.

The pantograph structure constructed about the balancer 18 compensates,in perfect conditions, the disturbances of the horizontal forces of alltypes to which it is subjected. As a result, the relationship betweenthe actuator and the force on the bows which it creates remainsvirtually independent of the speed of the train, the direction of travelof the pantograph and its unfolded height.

The motorisation means 90 substantially allows the inertial forcesrequired for the vertical movement of the structure to be accommodated.These motorisation means have particularly high dynamic performance. Ifnecessary, they can compensate the residual forces caused, inparticular, by the penetration through the air of the pantographstructure, preferably in coordination with the aerofoil 82 describedhereinbefore. This is why these motorisation means 90 are advantageouslycombined with the pantograph with the aerofoil, as shown in FIG. 6.Furthermore, these motorisation means similarly compensate, ifnecessary, all or a portion of the balancing or generate all or aportion of the forces of the bows on the catenary.

According to the invention, the kinematic chain of the servocontrolmeans is homokinetic. Therefore, whatever the position of thepantograph, the mechanical gain between the driving torque and thelinear acceleration of the bows will be virtually constant.

These kinematics are achieved by recreating a connecting rod/cranksystem (crank 108) which transforms a constant force into a sinusoidaltorque, which torque is retransformed into a constant force by thepantograph structure in the region of the bows 76 and 78.

Under these circumstances, the sinusoid of the crank 108 issynchronised, in other words in phase, with that of the pantograph.

The reduction gear 98 (FIG. 5) advantageously consists of a reductiongear having trains of pinions in an inverse relationship with that ofthe amplification between the pantograph structure and the crank (crank108) of the motorisation means.

The endless screw 102 is advantageously a screw of the reversible typewith a high reverse yield. Accordingly, it is preferable to use a ballscrew with rolled threads, preferably a screw having a diameter of 30 mmand a pitch of 30 mm.

In the example shown, the screw is reversible, and this is why areduction gear is also provided. In a variation, however, it is possibleto use a screw with a smaller pitch without a reduction gear but ofwhich the reverse yield would be lower.

The clutch 100 allows the motorisation means 90 to be disengaged, forexample in the event of a breakdown thereof, to allow impaired travel ofthe pantograph. This means that the performance of the pantograph wouldbe similar to that of a pantograph without servocontrol in such a modeof operation.

Referring now to FIG. 7, an example of servocontrol means 110 will bedescribed. FIG. 7 shows the motor 94 and the tachymetric dynamo 96. Thetachymetric dynamo driven by the motor transmits a speed signal SV.

The circuit 110 also comprises a first operational amplifier 114 (speedloop) receiving this speed signal SV and producing a first output signalS1 which is transmitted to a second operational amplifier 116 (currentloop). This second operational amplifier transmits a second outputsignal S2 which is received by a power amplifier 118 which transmits anoutput current CS sent to the electric motor 94 and of which the imageis sent to the second operational amplifier 116. The force sensor 112(carried by the pantograph bows) transmits a control signal SC which isapplied to the input of the second operational amplifier 116.

Thus, the control of the bow/catenary force is applied to the region ofthe current loop of the servocontrol means (operational amplifier 116).This results in a very short response time of the assembly andmanagement of perfectly homogeneous values since the torque transmittedby the motor 94 is proportional to the control signal of this loop.

An unfolding and folding operation 120 is also provided, which iscapable of receiving a control signal SRD applied to the firstoperational amplifier (speed loop) to bring about the folding orunfolding of the articulated mechanism 10, in other words in the exampleof the pantograph.

In addition, an emergency signal SU is sent by a safety device 122operating in the event of breakage of the catenary. This safety devicesends the emergency signal to fold the pantograph structure in any ofthe following cases (given as examples):

-   prolonged disappearance of the bow/catenary force in the operating    phase,-   ill-timed arrival of the structure at its high point,-   prolonged disappearance of the current supplying the power unit,-   transmission of the emergency signal by any other detection system.

In certain cases it may be worth performing a corrective action betweenthe signal SC transmitted by the force sensor and the actual forceexerted by the bows on the catenary. Therefore, it takes account of theinertial forces due to the mechanics placed downstream of the sensor andin particular to the bows. Corrective means 124 are provided for thispurpose, which are capable of transmitting a corrective action betweenthe control signal SC transmitted by the force sensor 112 and the actualforce exerted on the load F, or on the catenary in this case. Thesecorrective means comprise differentiating means capable ofdifferentiating the variations of speed recorded on the tachymetricdynamo 96 over time and of applying them to the input of the secondoperational amplifier 116. This signal, which is linear on acceleration,will generate a current and therefore a torque which is capable ofcompensating the above-defined inertial forces which are themselvesproportional to said acceleration.

The servocontrol system used as an ancillary for the folding orunfolding of the structure, as already mentioned, is duplicated byanother system for folding the pantograph in the event of failure of thefirst system, for example by the additional motorisation means 40 shownin FIG. 2.

It must be understood that the motorisation means with servocontrol, asdescribed hereinbefore, may be used in combination with other balancingmeans. In addition, they are not limited to use with an articulatedmechanism of the railway pantograph type.

To assist understanding of the drawing (FIG. 6), the servocontrolmotorisation system has been disposed vertically on the axis carryingthe aerofoil. In practice, and to save space, this motorisation systemwill be mounted on either of the two output shafts of the balancer andwill be disposed horizontally at its side.

It will be appreciated that the subject of the invention has numerousapplications, in particular for handling devices, transfer devices,railway pantographs, etc.

The balancing means of the device of the invention advantageously employa balancer of the type described by the aforementioned French patent No.88 02 423.

It is obviously possible to use other balancing means, providing thatthey have a high bandwidth.

1. Device for balancing a force, the device comprising: an articulated mechanism including: a proximal arm carried by a support and keyed on a first hinge pin; and a distal arm carried by the proximal arm and keyed on a second hinge pin extending parallel to the first hinge pin, the distal arm having a free end carrying a load; a balancer including: a first high bandwidth balancing means having a first output shaft and acting on the proximal arm; and a second high bandwidth balancing means having a second output shaft and acting on the distal arm ; and a high bandwidth coordinating means interposed between the first high bandwidth balancing means and the second high bandwidth balancing means to coordinate a rotational movement of the proximal arm with a rotational movement of the distal arm.
 2. The device of claim 1, wherein the balancer is capable of providing a sinusoidal mechanical torque, wherein a speed of rotation of the first output shaft is synchronized with a speed of rotation of the second output shaft, wherein a direction of rotation of the first output shaft is opposite to a direction of rotation of the second output shaft, and wherein the first output shaft is rotationally engaged with the first hinge pin and the second output shaft is rotationally engaged with the second hinge pin.
 3. Device according to claim 1 wherein the balancing means comprise motorisation means.
 4. The device of claim 1, wherein the first output shaft forms the first hinge pin of the proximal arm , and wherein the second output shaft is coupled to the second hinge pin of the distal arm by a transmission means, the transmission means having at least one deformable parallelogram.
 5. The device of claim 1, wherein the proximal arm and the distal arm have a same length.
 6. Device according to claim 1, further comprising an additional motorisation means formed by at least one actuator coupled to at least one moving part of the device.
 7. Device according to claim 6, wherein the additional motorisation means is capable of moving the articulated mechanism from one of two positions, which include a service position and a storage position, to the other position.
 8. Device according to claim 1, further comprising an additional motorisation means controlled by a force sensor placed at a position which is selected for assisting an operator in case of a manual displacement or to apply a constant force to a given part.
 9. Device according to claim 1, wherein the free end of the distal arm carries the bows of a pantograph capable of collecting the electrical energy from a catenary such that the load is formed by the force exerted on the catenary by the bows.
 10. Device according to claim 9, further comprising at least one accessory rotationally engaged with the second output shaft while being mounted either on the second output shaft or idly on the first output shaft, which has a selected geometry and moves parallel to the distal arm with which it is rotationally engaged, the accessory being disposed on a radius of gyration such that its penetration of the air generates a torque equal and opposed to the torque of penetration of the air of the articulated mechanism.
 11. Device according to claim 1, further comprising a servocontrol motorisation means comprising an electric motor coupled to an endless screw cooperating with a nut, the nut being carried by a crank coupled to one of the first output shaft and the second output shaft, and a servocontrol means to control the electric motor using a signal from a force sensor carried at the free end of the distal arm.
 12. Device according to claim 11, wherein the endless screw is a reversible screw driven by the electric motor via a reduction gear and a clutch mechanism interposed between the reduction gear and the endless screw.
 13. Device according to claim 11, wherein the servocontrol means comprise a tachymetric dynamo driven by the electric motor and capable of transmitting an output signal, a first operational amplifier receiving the speed signal and producing a first output signal, a second operational amplifier receiving the first output signal and transmitting a second output signal, a power amplifier receiving the second output signal and transmitting an output current sent to the electric motor wherein a control signal transmitted by the force sensor is applied to the input of the second operational amplifier.
 14. Device according to claim 13 wherein the servocontrol motorisation means forms an ancillary system for folding and unfolding of the articulated mechanism.
 15. Device according to claim 14, wherein the ancillary system for folding and unfolding is capable of receiving a control signal applied to the first operational amplifier to bring about the folding or unfolding of the articulated mechanism, the control signal having priority over the signal from the force sensor brought to the current loop.
 16. Device according to claim 14, wherein the ancillary system for folding and unfolding is capable of receiving an emergency signal applied to the first operational amplifier to bring about the folding of the articulated mechanism in an emergency, the emergency signal having priority over the signal from the force sensor brought to the current loop.
 17. Device according to claim 13, wherein the servocontrol means comprise corrective means capable of performing a corrective action between the control signal transmitted by the force sensor and the actual force applied to the load, the corrective means comprising differentiating means capable of differentiating the speed variations recorded on the tachymetric dynamo over time and applying the speed variations to the input of the second operational amplifier. 